1. Field of the Invention
This invention generally relates to a car navigation system for navigating the driver of a vehicle to a destination by giving a voice guidance or announcement.
2. Prior Art
Conventionally, car navigation systems are well known as an apparatus for navigating or guiding a vehicle (i.e. the driver of a vehicle) to an intended destination. In such systems, an appropriate present position detecting means, such as a GPS receiver, obtains the information relating to the position of a concerned vehicle. An appropriate memory means, such as CD-ROM, stores map (geographical) information. A map covering a neighboring area of the vehicle is read out from this memory means and displayed on a display means, such as a liquid crystal monitor.
An optimum route connecting a predetermined departure point and a predetermined destination is calculated by a route retrieving means. Based on the vehicle positional information and the calculated optimum route, an advancing direction of the vehicle is guided by both sound and screen display when the vehicle approaches each intersection. Such a conventional car navigation system is for example disclosed in Unexamined Japanese Patent Application No. HEI 2-6714, published in 1990.
FIG. 4 is a schematic block diagram showing an arrangement of such a conventional car navigation system which navigates the driver of a vehicle to his/her destination by giving a voice guidance. As shown in FIG. 4, the typical conventional car navigation system comprises a present position detecting means 1, a navigation control means 2, an information recording medium 3, a recording medium reproducing means 4, a display means 5, an operating means 6, a sound reproducing means 7, and a speaker 8.
Next, an operation of this conventional car navigation system will be explained. In FIG. 4, present position detecting means 1 comprises a GPS antenna and a GPS receiver processing apparatus. The present locational information, such as the present position of a vehicle, an advancing direction and a shifting speed, are calculated based on GPS signals. These information are sent to navigation control means 2.
Navigation control means 2 requests recording medium reproducing means 4 to provide map information covering the neighboring area of the present position based on the present locational information sent from present position detecting means 1. Recording medium reproducing means 4, when it receives the intended map information from information recording medium 3, sends this map information to navigation control means 2. Navigation control means 2 displays the received map information on display means 5 together with the present locational information.
Furthermore, navigation control means 2 calculates an optimum route from a predetermined departure point to a predetermined destination based on the map information sent from recording medium reproducing means 4 in response to a user's request entered through operating means 6.
Then, navigation control means 2 calculates the advancing direction of a vehicle when it approaches a next-coming intersection based on the route calculated and the present locational information. Sound reproducing means 7 generates a voice guidance through speaker 8. In this case, a predetermined voice announcement memorized beforehand in sound reproducing means 7 is produced from speaker 8. For example, when the vehicle needs to turn right at the intersection, speaker 8 generates a voice announcement such as "turn right|" On the other hand, when the vehicle needs to turn left at the intersection, speaker 8 generates a voice announcement such as "turn left|"
However, according to the above-described conventional car navigation system, there is the possibility that the driver of a vehicle may fail to listen to the voice guidance. In such a case, the driver will be forced to watch the screen of display means 5 to confirm the guidance, or he/she needs to operate a switch to re-generate the voice announcement.